Thermocompression bonding systems and methods of operating the same

ABSTRACT

A thermocompression bonding system for bonding semiconductor elements is provided. The thermocompression bonding system includes (1) a bond head assembly including a heater for heating an semiconductor element to be bonded, the bond head assembly including a fluid path configured to receive a cooling fluid; (2) a pressurized cooling fluid source; (3) a booster pump for receiving a pressurized cooling fluid from the pressurized cooling fluid source, and for increasing a pressure of the received pressurized cooling fluid; (4) a pressurized fluid reservoir for receiving pressurized cooling fluid from the booster pump; and (5) a control valve for controlling a supply of pressurized cooling fluid from the pressurized fluid reservoir to the fluid path.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/627,210, filed Feb. 20, 2015, which claims the benefit of U.S.Provisional Patent Application No. 61/945,916 filed Feb. 28, 2014, thecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the formation of electricalinterconnections in semiconductor packages, and more particularly, toimproved thermocompression bonding systems and methods of operating thesame.

BACKGROUND OF THE INVENTION

In certain aspects of the semiconductor packaging industry,semiconductor elements are bonded to bonding locations. For example, inconventional die attach (also known as die bonding) applications, asemiconductor die is bonded to a bonding location of a substrate (e.g.,a leadframe, another die in stacked die applications, a spacer, etc.).In advanced packaging applications, semiconductor elements (e.g., baresemiconductor die, packaged semiconductor die, etc.) are bonded tobonding locations of a substrate (e.g., a leadframe, a PCB, a carrier, asemiconductor wafer, a BGA substrate, etc.). Conductive structures(e.g., conductive bumps, contact pads, solder bumps, conductive pillars,copper pillars, etc.) provide electrical interconnection between thesemiconductor elements and the bonding locations. In certainapplications these conductive structures may provide electricalinterconnections analogous to wire loops formed using a wire bondingmachine.

In many applications (e.g., thermocompression bonding of semiconductorelements), solder material is included in the conductive structures. Inmany such processes, heat is applied to the semiconductor element beingbonded (e.g., through a heater in a bond head assembly carrying the bondtool). It is important that the application of heat be accomplishedquickly, such that the machine throughput (e.g., UPH, or units per hour)is at an acceptable level. This can be challenging as the heater (orparts of the heater) is desirably at different temperatures at differenttimes/locations (e.g., a cooler temperature during removal of thecomponent from a source, such as a wafer, as opposed to a warmertemperature at the time of thermocompressive bonding).

Thus, it would be desirable to provide improved methods for operatingbonding machines for bonding semiconductor elements.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, athermocompression bonding system for bonding semiconductor elements isprovided. The thermocompression bonding system includes (1) a bond headassembly including a heater for heating an semiconductor element to bebonded, the bond head assembly including a fluid path configured toreceive a cooling fluid; (2) a pressurized cooling fluid source; (3) abooster pump for receiving a pressurized cooling fluid from thepressurized cooling fluid source, and for increasing a pressure of thereceived pressurized cooling fluid; (4) a pressurized fluid reservoirfor receiving pressurized cooling fluid from the booster pump; and (5) acontrol valve for controlling a supply of pressurized cooling fluid fromthe pressurized fluid reservoir to the fluid path.

According to another exemplary embodiment of the present invention,another thermocompression bonding system for bonding semiconductorelements is provided. The thermocompression bonding system includes: abond head assembly including a heater for heating a semiconductorelement to be bonded, the bond head assembly including a fluid pathconfigured to receive a cooling fluid; a pressurized cooling fluidsource; a flow control valve for controlling a supply of pressurizedcooling fluid from the pressurized fluid source to the fluid path; and acomputer for controlling the flow control valve, the computer beingconfigured to control the supply of pressurized cooling fluid providedto the fluid path to be different during different stages of a coolingprocess of a thermocompression bonding process. Such a thermocompressionbonding system may also include various other elements described hereinincluding, for example, a booster pump, a pressurized fluid reservoir, acontrol valve (e.g., a digital on/off valve), a temperature sensor,amongst others.

According to yet another exemplary embodiment of the present invention,a method of operating a thermocompression bonding machine is provided.The method includes the steps of: (a) providing a pressurized coolingfluid source; (b) increasing a pressure of a pressurized cooling fluidfrom the pressurized cooling fluid source using a booster pump; (c)receiving pressurized cooling fluid from the booster pump at apressurized fluid reservoir; and (d) controlling, with a control valve,a flow of the pressurized cooling fluid from the pressurized fluidreservoir to a fluid path included in a bond head assembly of thethermocompression bonding machine.

According to yet another exemplary embodiment of the present invention,a method of operating a thermocompression bonding system is provided.The method includes the steps of: (a) providing a pressurized coolingfluid source; and (b) controlling, with a flow control valve, a supplyof pressurized cooling fluid from the pressurized cooling fluid sourceto a fluid path included in a bond head assembly of thethermocompression bonding system, the supply of pressurized coolingfluid provided to the fluid path being controlled by the flow controlvalve to be different during different stages of a cooling process of athermocompression bonding process. Of course, such a method may includeother steps as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1B are block diagram views of portions of an thermocompressionbonding machine illustrating a structure and method of bonding asemiconductor element to a substrate in accordance with an exemplaryembodiment of the present invention;

FIGS. 2-7 are block diagram views illustrating thermocompression bondingsystems in accordance with various exemplary embodiments of the presentinvention;

FIG. 8, FIGS. 9A-9B, FIG. 10, and FIG. 11 are graphical illustrations oftemperature profiles of elements of thermocompression bonding systems inaccordance with various exemplary embodiments of the present invention;and

FIGS. 12-17 are flow diagrams illustrating methods of operatingthermocompression bonding systems in accordance with various exemplaryembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “semiconductor element” is intended to refer toany structure including (or configured to include at a later step) asemiconductor chip or die. Exemplary semiconductor elements include abare semiconductor die, a semiconductor die on a substrate (e.g., aleadframe, a PCB, a carrier, a semiconductor chip, a semicondcutorwafer, a BGA substrate, a semiconductor element, etc.), a packagedsemiconductor device, a flip chip semiconductor device, a die embeddedin a substrate, a stack of semiconductor die, amongst others. Further,the semiconductor element may include an element configured to be bondedor otherwise included in a semiconductor package (e.g., a spacer to bebonded in a stacked die configuration, a substrate, etc.).

As used herein, the terms “substrate” and “workpiece” are intended torefer to any structure to which a semiconductor element may be bonded(e.g., thermocompressively bonded, ultrasonically bonded,thermosonically bonded, die bonded, etc.). Exemplary substrates include,for example, a leadframe, a PCB, a carrier, a semiconductor chip, asemicondcutor wafer, a BGA substrate, a semiconductor element, etc.

In accordance with certain aspects of the present invention,thermocompression bonding systems utilizing heat in a bond headassembly, for example, for melting and/or softening of a solder materialincluded as part of the interconnects of a semiconductor element to bebonded, are disclosed. A bond tool (which may be distinct from theheater, or which may be part of the heater) carried by the bond headassembly places and bonds a semiconductor element to a substrate bymelting and re-solidifying solder bumps on the semiconductor elementbeing placed/bonded. In order to melt the solder bumps, it is importantto be able to rapidly heat the bond tool. It is also desirable to beable to rapidly cool the bond tool while maintaining the position of thesemiconductor element being bonded (e.g., to single digit micron, orsmaller, levels). Thus, it is desirable that thermocompression bondingsystems (and related processes) be capable of precise control of thebond tool temperature during all phases of the bonding process (e.g.,during the heating phase/process, during the cooling phase/process,etc.).

According to various aspects of the present invention, the bond headtemperature (e.g., part of the bond head such as the heater/bond tool)may be controlled during the cooling phase/process of athermocompression bonding process. For example, according to certainexemplary embodiments of the present invention, the flow rate ofpressurized cooling fluid may be controlled (e.g., controlled to be avariable cooling rate as commanded by a computer program, for example,using a command profile with a measured temperature as a feedbacksignal) using an analog flow control valve. This may be particularlybeneficial because during a thermocompression bonding process there areoften times when cooling rates other than maximum system capability aredesired for the control of the bonding process. For example, during theinitial solidification (i.e., re-solidification after melting) of thesolder, highly controlled (and repeatable) cooling is desirable toprovide bonded interconnections of a substantially consistent quality.

A temperature sensor (e.g., a feedback sensor positioned to sense thetemperature of, for example, a lower surface of the heater/bond tool)may be provided within a thermocompression bond head assembly during acommanded rapid cooling stage of a cooling process (e.g., 100-150° C.over a 1 second period). Such feedback controlled cooling may be used inconnection with a multi-stage cooling process as described herein (e.g.,a first controlled cooling stage at less than maximum cooling, and asecond cooling stage at maximum cooling).

Further, such feedback controlled cooling may also be used at varioustimes during a thermocompression bonding process. For example, a certainamount of heat (thermal energy) remains within portions of the bond headassembly not directly measured by the temperature feedback sensor. Thisthermal energy will gradually move from the warmer bodies to the justcooled body (e.g., the heater/bond tool). This appears as a drift oftemperature on the temperature feedback device. In such a circumstance,it may be undesirable to use a digital (e.g., on/off) cooling system inthis circumstance as the amount of cooling is not easily controlled,resulting in a portion of the bond head assembly being cooled to anundesirable amount.

According to various aspects of the present invention, a booster pump(e.g., a mechanical pressure booster) may be provided to increase theincoming pressurized cooling fluid above that which is normallyavailable (e.g., factory compressed air). Such an increase in theincoming pressure may be used to overcome pressure drop in smallchannels in the heater. The pressure drops though such channels,primarily caused by friction of the channel walls, causes the fluidvelocity to drop rapidly leading to a loss of cooling efficiency. Such aloss may be mitigated by the use of higher pressure fluid. Often thepressure available in a facility (e.g., compressed air) is not highenough to provide maximum cooling. By providing a pressure booster, theinput cooling fluid pressure may be raised to a desired level (e.g., apressure increase of at least 50%, a pressure increase of at least 100%,etc., with a specific example being a 100% increase such as an increasefrom 0.6 MPa to 1.2 MPa).

Referring now to the drawings, FIG. 1A illustrates portions of bondingmachine 100 (e.g., a thermocompression flip chip bonding machine)including bond stage 120 (e.g., a shuttle, a heated shuttle, a heatblock, an anvil, etc.), and support structure 104 supported by bondstage 120 (where support structure 104 and bond stage 120 may beintegrated into a single element). As will be appreciated by thoseskilled in the art, support structure 104 may be referred to as anapplication specific part (sometimes referred to in the industry as ap-part). Substrate 102 is supported by support structure 104, and isconfigured to receive at least one semiconductor element through athermocompression bonding process. Lower conductive structures 108 a,108 b (e.g., conductive traces, conductive pads, etc.) are provided onsubstrate 102. Bonding machine 100 also includes bond head assembly 122which carries heated bond tool 112 that carries semiconductor element110. Upper conductive structures 114 a, 114 b (e.g., conductive pillarssuch as copper pillars, shown including solder contact portions 116 a,116 b) are provided on semiconductor element 110. Bond tool 112 islowered such that upper conductive structures 114 a, 114 b contact lowerconductive structures 108 a, 108 b (e.g., see FIG. 1B). As illustratedin FIG. 1B, through a thermocompressive bonding process, solder contactportions 116 a, 116 b are softened, and then re-solidified as solderinterfaces 118 a, 118 b, providing a permanent conductive couplingbetween ones of upper conductive structures 114 a, 114 b and respectivelower conductive structures 108 a, 108 b. Although FIGS. 1A-1Billustrate only two pairs of conductive structures (pair 114 a, 108 aand pair 114 b, 108 b), this is of course a simple example for ease ofexplanation. In practice, any number of pairs of conductive structuresmay be provided (e.g., tens of conductive structure pairs, hundreds ofconductive structure pairs, etc.).

FIG. 2 illustrates exemplary thermocompression bonding system 200including thermocompression bonding machine 240. Machine 240 includesbond head assembly 220 including upper structure 221 (including variouselements, not shown), cooling structure 222 and heater 224. Heater 224is in contact with semiconductor element 228 (e.g., a semiconductor dieto be bonded). As will be appreciated by those skilled in the art,heater 224 may be a heated bond tool configured to carry and bondsemiconductor element 228 to workpiece 260. As will be appreciated bythose skilled in the art, heater 224 may be considered a heated bondtool (similar to tool 112 illustrated in FIGS. 1A-1B). That is, theterms heater and bond tool may be used interchangeably, and may beintegrated into a single component (as shown in the exemplary embodimentillustrated in FIGS. 1A-1B and FIGS. 2-7) or may be multiple separatecomponents. Machine 240 also includes computer 236, and bond stage 232for supporting workpiece 260. Temperature sensor 226 measures thetemperature of heater 224, and provides information related to thistemperature back to computer 236 as temperature signal 234.

Thermocompression bonding system 200 also includes an element forproviding a pressurized cooling fluid (e.g., compressed air) to bondhead 220 for cooling heater/bond tool 224 as part of a thermocompressionbonding process. More specifically, system 200 includes pressurizedcooling fluid source 202 (e.g., a factory compressed air source, such aspiping from a compressed air tank or compressor, etc.) for providingpressurized cooling fluid to booster pump 204. Booster pump 204 receivespressurized cooling fluid from source 202, and increases a pressure ofthe received pressurized cooling fluid. In certain exemplary embodimentsof the present invention, booster pump 204 increases the pressure of thepressurized cooling fluid from source 202 by at least 50%, by at least100%, etc. In one very specific example, pressurized cooling fluid fromsource 202 is provided at a pressure of approximately 0.6 MPa, andbooster pump 204 increases the pressure of the pressurized cooling fluidto approximately 1.2 MPa (e.g., a pressure increase of approximately100%). The pressurized cooling fluid (at the now increased pressure) isthen received by pressurized fluid reservoir 206 (e.g., a compressed airtank). Pressurized fluid from reservoir 206 is received by flow controlvalve 208 (e.g., an analog control valve), where flow control valve 208is configured to adjust a pressure of the pressurized cooling fluidprovided to bond head assembly 220. Downstream of flow control valve 208is control valve 210 (e.g., an on/off digital valve) for controlling asupply of pressurized cooling fluid to bond head assembly 220. Flowcontrol valve 208 and control valve 210 are each controlled by computer236 (as shown by respective control signals 238 a, 238 b). Downstream ofvalve 210, the pressurized cooling fluid travels within fluid path 212until it reaches inlet 214 of bond head assembly 220. Fluid path 215 isincluded within bond head assembly 220, and includes inlet fluid path216 (defined by upper structure 221), cooling path 222 a (defined bycooling structure 222), and outlet fluid path 218 (defined by upperstructure 221).

In accordance with the exemplary embodiments of the present inventionillustrated and described in connection with FIGS. 2-7, various elementsare described as being part of a thermocompression bonding system (e.g.,systems 200, 300, 400, 500, 600, and 700) but distinct from thecorresponding thermcompression bonding machine (e.g., machines 240, 340,440, 540, 640, and 740). Examples of such elements in FIG. 2 areelements 204, 206, 208, and 210. In accordance with the presentinvention, any or all of such elements may be included in thecorresponding thermocompression bonding machine.

Each of FIGS. 3-7 illustrate systems similar to system 200 shown in FIG.2, with like elements being numbered including the same reference numberexcept with a different initial digit. For example, the bond headassemblies are numbered as element 220 (in FIG. 2), element 320 (in FIG.3), element 420 (in FIG. 4), element 520 (in FIG. 5), element 620 (inFIG. 6), element 720 (in FIG. 7). Absent a difference noted below, theelement (and its function) is substantially similar to those describedin FIG. 2.

Referring specifically to FIG. 3, the primary difference compared toFIG. 2 is that flow control valve 308 is positioned downstream ofcontrol valve 310 (as opposed to flow control valve 208 being positionedupstream of control valve 210 in FIG. 2). FIG. 3 illustrates exemplarythermocompression bonding system 300 including thermocompression bondingmachine 340. Machine 340 includes bond head assembly 320 including upperstructure 321, cooling structure 322 and heater 324. Heater 324 is incontact with semiconductor element 328. As will be appreciated by thoseskilled in the art, heater 324 may be a heated bond tool configured tocarry and bond semiconductor element 328 to workpiece 360. Machine 340also includes computer 336, and bond stage 332 for supporting workpiece360. Temperature sensor 326 measures the temperature of heater 324, andprovides information related to this temperature back to computer 336 astemperature signal 334.

Thermocompression bonding system 300 also includes pressurized coolingfluid source 302 for providing pressurized cooling fluid to booster pump304. Booster pump 304 receives pressurized cooling fluid from source302, and increases a pressure of the received pressurized cooling fluid(e.g., by at least 50%, by at least 100%, etc.). The pressurized coolingfluid (at the now increased pressure) is then received by pressurizedfluid reservoir 306. Pressurized fluid from reservoir 306 is received bycontrol valve 310 (e.g., an on/off digital valve) for controlling asupply of pressurized cooling fluid to bond head assembly 320.Downstream of control valve 310 is flow control valve 308 (e.g., ananalog control valve), where flow control valve 308 is configured toadjust a pressure of the pressurized cooling fluid provided to bond headassembly 320. Control valve 310 and flow control valve 308 are eachcontrolled by computer 336, as shown by respective control signals 338a, 338 b). Downstream of flow control valve 308, the pressurized coolingfluid travels within fluid path 312 until it reaches inlet 314 of bondhead assembly 320. Fluid path 315 is included within bond head assembly320, and includes inlet fluid path 316 (defined by upper structure 321),cooling path 322 a (defined by cooling structure 322), and outlet fluidpath 318 (defined by upper structure 321).

Referring specifically to FIG. 4, the primary difference compared toFIGS. 2-3 is that flow control valve 408 is in a parallel fluid pathwith a fluid path including control valve 410 (as opposed to flowcontrol valves 208/308 being in line with control valves 210/310 inFIGS. 2-3, respectively). FIG. 4 illustrates exemplary thermocompressionbonding system 400 including thermocompression bonding machine 440.Machine 440 includes bond head assembly 420 including upper structure421, cooling structure 422 and heater 424. Heater 424 is in contact withsemiconductor element 428. As will be appreciated by those skilled inthe art, heater 424 may be a heated bond tool configured to carry andbond semiconductor element 428 to workpiece 460. Machine 440 alsoincludes computer 436, and bond stage 432 for supporting workpiece 460.Temperature sensor 426 measures the temperature of heater 424, andprovides information related to this temperature back to computer 436 astemperature signal 434.

Thermocompression bonding system 400 also includes pressurized coolingfluid source 402 for providing pressurized cooling fluid to booster pump404. Booster pump 404 receives pressurized cooling fluid from source402, and increases a pressure of the received pressurized cooling fluid(e.g., by at least 50%, by at least 100%, etc.). The pressurized coolingfluid (at the now increased pressure) is then received by pressurizedfluid reservoir 406. Pressurized fluid from reservoir 406 may flow ineither of two directions (or perhaps both, if desired): a firstdirection through control valve 410 (e.g., an on/off digital valve) tofluid path 412; and a second direction through flow control valve 408(e.g., an analog control valve) to fluid path 412. For example,depending upon the specific application (and/or depending on thetiming/stage of a bonding process), it may be desirable to have acontinuous maximum flow of pressurized cooling fluid, in which casecontrol valve 410 may be open (and flow control valve 408 is closed). Inanother application, (and/or depending on the timing/stage of a bondingprocess), it may be desirable to have a controlled (e.g., analogcontrolled) flow of pressurized cooling fluid at a specific pressurevalue, in which case control valve 410 may be closed (and flow controlvalve 408 open at selected positions to provide the desired pressurevalues). Flow control valve 408 and control valve 410 are eachcontrolled by computer 436, as shown by respective control signals 438a, 438 b). Regardless of which direction the pressurized cooling fluidflows (i.e., either through valve 410, or through valve 408), thepressurized cooling fluid travels within fluid path 412 until it reachesinlet 414 of bond head assembly 420. Fluid path 415 is included withinbond head assembly 420, and includes inlet fluid path 416 (defined byupper structure 421), cooling path 422 a (defined by cooling structure422), and outlet fluid path 418 (defined by upper structure 421).

In FIG. 4, it is noteworthy that flow control valve 408 receivespressurized cooling fluid after the pressure of the fluid has beenincreased by booster pump 404. Thus, depending on design considerations,flow control valve 408 may be able to provide pressurized cooling fluidat a pressure level up to the maximum output pressure of booster pump406 (e.g., or as low as desired given design constraints, using analogcontrol). Referring specifically to FIG. 5, the primary differencecompared to FIG. 4 is that flow control valve 508 receives its inputcooling fluid from source 502 before the pressure of the fluid has beenincreased by booster pump 504. Therefore, the pressurized cooling fluidis provided at a lower pressure (as opposed to FIG. 4, where the inputcooling fluid from source 402 is provided at a higher level, downstreamof booster pump 404).

FIG. 5 illustrates exemplary thermocompression bonding system 500including thermocompression bonding machine 540. Machine 540 includesbond head assembly 520 including upper structure 521, cooling structure522 and heater 524. Heater 524 is in contact with semiconductor element528. As will be appreciated by those skilled in the art, heater 524 maybe a heated bond tool configured to carry and bond semiconductor element528 to workpiece 560. Machine 540 also includes computer 536, and bondstage 532 for supporting workpiece 560. Temperature sensor 526 measuresthe temperature of heater 524, and provides information related to thistemperature back to computer 536 as temperature signal 534.

Thermocompression bonding system 500 also includes pressurized coolingfluid source 502 for providing pressurized cooling fluid to booster pump504, and/or to flow control valve 508. Booster pump 504 receivespressurized cooling fluid from source 502, and increases a pressure ofthe received pressurized cooling fluid (e.g., by at least 50%, by atleast 100%, etc.). The pressurized cooling fluid (at the now increasedpressure) is then received by pressurized fluid reservoir 506.Pressurized fluid from reservoir 506 flows through control valve 510(e.g., an on/off digital valve) to fluid path 512. For example,depending upon the specific application (and/or depending on thetiming/stage of a bonding process), it may be desirable to have acontinuous maximum flow of pressurized cooling fluid, in which casecontrol valve 510 may be open (and flow control valve 508 is closed). Inanother application, (and/or depending on the timing/stage of a bondingprocess), it may be desirable to have a controlled (e.g., analogcontrolled) flow of pressurized cooling fluid at a specific pressurevalue, in which case control valve 510 may be closed (and flow controlvalve 508 open at selected positions to provide the desired flowvalues). Flow control valve 508 and control valve 510 are eachcontrolled by computer 536, as shown by respective control signals 538a, 538 b). Regardless of which valve controls the flow of thepressurized cooling fluid (i.e., valve 510 or valve 508), thepressurized cooling fluid travels within fluid path 512 until it reachesinlet 514 of bond head assembly 520. Fluid path 515 is included withinbond head assembly 520, and includes inlet fluid path 516 (defined byupper structure 521), cooling path 522 a (defined by cooling structure522), and outlet fluid path 518 (defined by upper structure 521).

Each of the exemplary configurations shown in FIGS. 2-5 illustratethermocompression bonding systems including distinct control valves(e.g., digital “on/off” valves) and flow control valves (e.g., analogcontrol valves for controlling the supply of a pressurized cooling fluidaccording to a computer program of other profile). As will beappreciated by those skilled in the art, certain aspects of the presentinvention may be achieved with only one of these two valves included inthe system. FIGS. 6-7 illustrate two examples of such an arrangement.

Referring specifically to FIG. 6, the primary difference compared toFIG. 4 is that control of the pressurized cooling fluid is controlled byflow control valve 608 and not a corresponding digital on/off controlvalve (as opposed to FIG. 4, which includes both analog flow controlvalves 408 as well as an on/off control valve 410). For example, onemight consider an arrangement where a flow control valve is providedthat is robust enough to control the flow/supply of pressurized coolingfluid during all stages of a cooling phase/process of athermocompression bonding process. FIG. 6 illustrates exemplarythermocompression bonding system 600 including thermocompression bondingmachine 640. Machine 640 includes bond head assembly 620 including upperstructure 621, cooling structure 622 and heater 624. Heater 624 is incontact with semiconductor element 628. As will be appreciated by thoseskilled in the art, heater 624 may be a heated bond tool configured tocarry and bond semiconductor element 628 to workpiece 660. Machine 640also includes computer 636, and bond stage 632 for supporting workpiece660. Temperature sensor 626 measures the temperature of heater 624, andprovides information related to this temperature back to computer 636 astemperature signal 634.

Thermocompression bonding system 600 also includes pressurized coolingfluid source 602 for providing pressurized cooling fluid to booster pump604. Booster pump 604 receives pressurized cooling fluid from source602, and increases a pressure of the received pressurized cooling fluid(e.g., by at least 50%, by at least 100%, etc.). The pressurized coolingfluid (at the now increased pressure) is then received by pressurizedfluid reservoir 606. Pressurized cooling fluid is directed fromreservoir 606 to flow control valve 608. Flow control valve 608 controlsthe supply of pressurized cooling fluid (e.g., analog control accordingto a computer program where the flow/supply may be varied depending onthe timing/stage of a bonding process). Pressurized cooling fluid thatpasses through flow control valve 608 travels within fluid path 612until it reaches inlet 614 of bond head assembly 620. Fluid path 615 isincluded within bond head assembly 620, and includes inlet fluid path616 (defined by upper structure 621), cooling path 622 a (defined bycooling structure 622), and outlet fluid path 618 (defined by upperstructure 621).

Referring specifically to FIG. 7, the primary difference compared toFIG. 6 is that control of the pressurized cooling fluid is controlled bycontrol valve 710 and not a corresponding analog flow control valve (asopposed to FIG. 6, which includes flow control valve 608). For example,one might consider an application where analog control of the supply ofpressurized cooling fluid is not needed or desired, and that theaddition of a booster pump to increase the fluid pressure provides thedesired cooling via a simple digital on/off control valve. FIG. 7illustrates exemplary thermocompression bonding system 700 includingthermocompression bonding machine 740. Machine 740 includes bond headassembly 720 including upper structure 721, cooling structure 722 andheater 724. Heater 724 is in contact with semiconductor element 728. Aswill be appreciated by those skilled in the art, heater 724 may be aheated bond tool configured to carry and bond semiconductor element 728to workpiece 760. Machine 740 also includes computer 736, and bond stage732 for supporting workpiece 760. Temperature sensor 726 measures thetemperature of heater 724, and provides information related to thistemperature back to computer 736 as temperature signal 734.

Thermocompression bonding system 700 also includes pressurized coolingfluid source 702 for providing pressurized cooling fluid to booster pump704. Booster pump 704 receives pressurized cooling fluid from source702, and increases a pressure of the received pressurized cooling fluid(e.g., by at least 50%, by at least 100%, etc.). The pressurized coolingfluid (at the now increased pressure) is then received by pressurizedfluid reservoir 706. Pressurized cooling fluid is directed fromreservoir 706 to control valve 710. Control valve 710 controls the flowof pressurized cooling fluid (e.g., “on/off” digital control accordingto a computer program). Pressurized cooling fluid that passes throughcontrol valve 710 travels within fluid path 712 until it reaches inlet714 of bond head assembly 720. Fluid path 715 is included within bondhead assembly 720, and includes inlet fluid path 716 (defined by upperstructure 721), cooling path 722 a (defined by cooling structure 722),and outlet fluid path 718 (defined by upper structure 721).

As will be appreciated by those skilled in the art, the systemsillustrated in FIGS. 2-7 may include additional elements, or lesselements, according to certain exemplary embodiments of the presentinvention. An example of an additional element(s) may be a check valvefor preventing reverse flow of pressurized cooling fluid. An example ofan element(s) that may be removed from one of the systems depending onthe specific application may be the booster pump, the pressurized fluidreservoir, amongst others.

Each of FIGS. 2-7 illustrate exemplary fluid paths 215, 315, 415, 515,615, and 715 included within the respective bond head assembly. Thesefluid paths have each been illustrated in a simple manner to include aninlet fluid path, a cooling path defined by a cooling structure, and anoutlet fluid path; however, and as will be appreciated by those skilledin the art, the fluid path may be much more complex than thoseillustrated. That is, in thermocompression bonding systems, rapidheating and cooling of portions of the bond head assembly may becritical. Complex cooling systems, including many fluid channels, may beutilized.

Certain of the benefits of various exemplary embodiments of the presentinvention are graphically shown in FIG. 8, FIGS. 9A-9B, FIG. 10, andFIG. 11. Referring specifically to FIG. 8, a time versus temperatureplot is provided showing heating and cooling of solder material includedin interconnections formed in a thermocompression bonding process (e.g.,similar to solder material 116 a, 116 b shown in FIG. 1A) for twodifferent types of thermocompressive bonding systems. In thisillustration, the “Unit 1” system includes a booster pump (similar tobooster pumps 204, 304, 404, 504, 604 and 704 illustrated in FIGS. 2-7,respectively). The “Unit 2” system does not includes such a boosterpump, but rather relies on factory compressed air pressure. In thisexample, for both systems the heating process is identical, but thecooling processes are different because the pressurized cooling fluid inUnit 1 system is provided at a higher pressure. As shown in FIG. 8, theUnit 1 system cools faster compared to the Unit 2 system, andspecifically: reaches the critical melt/re-solidification temperaturefaster; and reaches the process complete temperature (approximately 70degrees) about 1 second faster (e.g., approximately 2.2 seconds for Unit1, versus 3.2 seconds for Unit 2). As will be appreciated by thoseskilled in the art, after this “process complete temperature” is reachedfurther processing (e.g., commencing the process to pick the nextsemiconductor element to be bonded) may commence. It will be appreciatedthat further processing (e.g., the process of picking the nextsemiconductor element to be bonded) may actually be commenced beforereaching the “process complete temperature”, for example, so long as there-solidification temperature has been reached. Thus, the fasterprocessing time of the Unit 1 system in accordance with the presentinvention results in an improved UPH rate.

Another important consideration in cooling the heater/bond tool inthermocompression bonding systems relates to process consistency. Forexample, it is very desirable that each system running the same processto reach the melt/re-solidification temperature at approximately thesame time during the process. However, even if designed to be the same,each thermocompression bonding system performs somewhat differently inpractice. FIG. 9A illustrates time versus temperature plots for twothermocompression bonding systems (i.e., “Unit 1” and “Unit 2”) of thesame design. As shown in FIG. 9A, and detailed in FIG. 9B, there is asubstantial time difference (i.e., T_(D)) between how long it takes Unit1, versus how long it takes Unit 2, to reach the re-solidificationtemperature. While the example shown in FIGS. 9A-9B has a larger thannormal variation (for ease of illustrating the problem), the resultantT_(D) is a real world portability issue in thermocompression bonding.

FIG. 10 illustrates a time versus temperature plot for a 2 stage coolingprocess on a thermocompression bonding system according to the presentinvention. As shown in FIG. 10, after the “Heating” process is completeat approximately 1.25 seconds, a “Controlled Cooling” stage of thecooling process begins. During this Controlled Cooling stage of thecooling process a cooling rate is defined by a computer program (and maybe feedback controlled, with the temperature signal being the feedbacksignal), and the bond head assembly (including the heater/bond tool) arecooled according to a predetermined cooling profile until apredetermined event occurs (e.g., until a predetermined temperature isdetected). In the example shown in FIG. 10, this predetermined event isthe cooling process reaching the re-solidification temperature. Afterreaching the re-solidification temperature, the “Max Cooling” stage ofthe cooling process begins and the maximum (or a predetermined maximum)amount of cooling is provided in order to reach the process completetemperature (e.g., approximately 70 degrees C. in FIG. 10) as soon aspossible. Using such a two stage cooling process, certain portabilityissues from one thermocompression bonding system to anotherthermocompression bonding system may be overcome. For example, FIG. 11illustrates time versus temperature plots for a 2 stage cooling processon 2 different thermocompression bonding systems (i.e., “Unit 1” and“Unit 2”). As shown in FIG. 11, using the 2 stage cooling process, eachsystem is able to reach the re-solidification temperature atapproximately the same time.

FIGS. 12-17 illustrate exemplary methods of operating thermocompressionbonding systems. As will be appreciated by those skilled in the art,certain steps may be added, certain steps may be deleted, and/or theorder of certain of the steps may be rearranged, within the scope of thepresent invention.

Referring specifically to FIG. 12, at Step 1200 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1202, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1204, apressure of a pressurized cooling fluid from the pressurized coolingfluid source is increased using a booster pump. At Step 1206,pressurized cooling fluid from the booster pump is received at apressurized fluid reservoir. At Step 1208, a flow of the pressurizedcooling fluid from the pressurized fluid reservoir is controlled using acontrol valve (e.g., an on/off digital control valve) to a fluid pathincluded in a bond head assembly of the thermocompression bondingmachine during a cooling phase/process of the thermocompression bondingprocess. For example, the arrangement of system 700 illustrated in FIG.7 may be used to perform the method of FIG. 12.

Referring specifically to FIG. 13, at Step 1300 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1302, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1304, apressure of a pressurized cooling fluid from the pressurized coolingfluid source is increased using a booster pump. At Step 1306,pressurized cooling fluid from the booster pump is received at apressurized fluid reservoir. At Step 1308, a flow of the pressurizedcooling fluid from the pressurized fluid reservoir is controlled using acontrol valve (e.g., an on/off digital control valve) to a fluid pathincluded in a bond head assembly of the thermocompression bondingmachine during a cooling phase/process of the thermocompression bondingprocess. At Step 1310, a supply of pressurized cooling fluid provided tothe fluid path is controlled using a flow control valve, positioned inline with the control valve, during the cooling phase/process of thethermocompression bonding process. For example, the arrangement ofsystems 200 and 300 illustrated in FIGS. 2-3, respectively, may be usedto perform the method of FIG. 13.

Referring specifically to FIG. 14, at Step 1400 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1402, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1404, asupply of the pressurized cooling fluid from the pressurized coolingfluid source to a fluid path included in a bond head assembly of thethermocompression bonding machine is controlled using a flow controlvalve during a cooling phase/process of the thermocompression bondingprocess. For example, the arrangement of system 600 illustrated in FIG.6 may be used to perform the method of FIG. 14.

Referring specifically to FIG. 15, at Step 1500 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1502, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1504, apressure of a pressurized cooling fluid from the pressurized coolingfluid source is increased using a booster pump. At Step 1506,pressurized cooling fluid from the booster pump is received at apressurized fluid reservoir. At Step 1508, a supply of the pressurizedcooling fluid from the pressurized fluid reservoir to a fluid pathincluded in a bond head assembly of the thermocompression bondingmachine is controlled using a flow control valve during a coolingphase/process of the thermocompression bonding process. For example, thearrangement of system 600 illustrated in FIG. 6 may be used to performthe method of FIG. 15.

Referring specifically to FIG. 16, at Step 1600 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1602, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1604, apressure of a pressurized cooling fluid from the pressurized coolingfluid source is increased using a booster pump. At Step 1606,pressurized cooling fluid from the booster pump is received at apressurized fluid reservoir. At Step 1608, a supply of pressurizedcooling fluid provided to the fluid path is adjusted using a flowcontrol valve during a first stage of a cooling phase/process of thethermocompression bonding process. At Step 1610, a flow of thepressurized cooling fluid from the pressurized fluid reservoir to afluid path included in a bond head assembly of the thermocompressionbonding machine is controlled using a control valve during a secondstage of the cooling phase/process of the thermocompression bondingprocess. For example, such a multi-stage cooling approach during thecooling phase/process of the thermocompression bonding process may yieldresults similar to those shown in FIGS. 10-11. For example, thearrangement of systems 400 and 500 illustrated in FIGS. 4-5 may be usedto perform the method of FIG. 16.

Referring specifically to FIG. 17, at Step 1700 a semiconductor elementcarried by a bond head assembly of a thermocompression bonding machineis heated with a heater during a heating phase/process of athermocompression bonding process. At Step 1702, a pressurized coolingfluid source (e.g., factory compressed air) is provided. At Step 1704, apressure of a pressurized cooling fluid from the pressurized coolingfluid source is increased using a booster pump. At Step 1706,pressurized cooling fluid from the booster pump is received at apressurized fluid reservoir. At Step 1708, a flow of the pressurizedcooling fluid to a fluid path included in a bond head assembly of thethermocompression bonding machine is controlled (with at least one of acontrol valve and a flow control valve) during a cooling phase/processof the thermocompression bonding process wherein the coolingphase/process includes a first stage and a second stage, and wherein asupply of the pressurized cooling fluid during the first stage isdifferent from the second stage. For example, the arrangement of system200, 300, 400, 500, and 600 illustrated in FIGS. 2-6, respectively, maybe used to perform the method of FIG. 17.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of operating a thermocompression bondingsystem, the method comprising the steps of: providing a pressurizedcooling fluid source; increasing a pressure of a pressurized coolingfluid from the pressurized cooling fluid source using a booster pump;receiving pressurized cooling fluid from the booster pump at apressurized fluid reservoir; and controlling, with a control valve, aflow of the pressurized cooling fluid from the pressurized fluidreservoir to a fluid path included in a bond head assembly of thethermocompression bonding system to be different during different stagesof a cooling phase of a bonding cycle of the thermocompression bondingsystem.
 2. The method of claim 1 further comprising the step ofadjusting a supply of pressurized cooling fluid provided to the fluidpath using a flow control valve.
 3. The method of claim 2 wherein theflow control valve is positioned in line with the control valve.
 4. Themethod of claim 3 wherein the flow control valve is positioneddownstream of the control valve in relation to the flow of thepressurized cooling fluid provided to the fluid path.
 5. The method ofclaim 3 wherein the flow control valve is positioned upstream of thecontrol valve in relation to the flow of the pressurized cooling fluidprovided to the fluid path.
 6. The method of claim 2 wherein the flowcontrol valve is positioned in parallel with a fluid path including thecontrol valve.
 7. The method of claim 2 further comprising the step ofproviding pressurized cooling fluid to the flow control valve using thebooster pump.
 8. The method of claim 2 wherein the flow control valve ispositioned in parallel with a fluid path including the booster pump, thepressurized fluid reservoir, and the control valve.
 9. The method ofclaim 2 further comprising the step of controlling at least one of thecontrol valve and the flow control valve using a computer.
 10. Themethod of claim 9 further comprising the steps of sensing a temperatureof a heater of the bond head assembly using a temperature sensor, andreceiving information related to the temperature of the heater sensed bythe temperature sensor using the computer.
 11. The method of claim 2wherein the flow control valve is an analog control valve.
 12. Themethod of claim 1 wherein the control valve is a digital on/off controlvalve.
 13. The method of claim 1 wherein a pressure of the pressurizedcooling fluid from the pressurized cooling fluid source is increasedusing the booster pump by at least 50%.
 14. The method of claim 1wherein the bond head assembly includes a bond tool for bonding asemiconductor element to a substrate, wherein a heater of the bond headassembly heats the semiconductor element by heating the bond tool, andwherein the heater is cooled by the pressurized cooling fluid providedto the fluid path.
 15. The method of claim 1 wherein the bond headassembly includes a heater configured as a bond tool for bonding asemiconductor element to a substrate, the heater being cooled by thepressurized cooling fluid being provided to the fluid path.